Abstract
Considerable effort has been made to parameterize turbulent kinetic energy (TKE) dissipation rate ε and mixing in buoyant plumes and stratified shear flows. Here, a parameterization based on Kunze et al. is examined, which estimates ε as the amount of energy contained in an unstable shear layer (Ri < Ric) that must be dissipated to increase the Richardson number Ri = N2/S2 to a critical value Ric within a turbulent decay time scale. Observations from the tidal Columbia River plume are used to quantitatively assess the relevant parameters controlling ε over a range of tidal and river discharge forcings. Observed ε is found to be characterized by Kunze et al.'s form within a factor of 2, while exhibiting slightly decreased skill near Ri = Ric. Observed dissipation rates are compared to estimates from a constant interfacial drag formulation that neglects the direct effects of stratification. This is found to be appropriate in energetic regimes when the bulk-averaged Richardson number Rib is less than Ric/4. However, when Rib > Ric/4, the effects of stratification must be included. Similarly, ε scaled by the bulk velocity and density differences over the plume displays a clear dependence on Rib, decreasing as Rib approaches Ric. The Kunze et al. ε parameterization is modified to form an expression for the nondimensional dissipation rate that is solely a function of Rib, displaying good agreement with the observations. It is suggested that this formulation is broadly applicable for unstable to marginally unstable stratified shear flows.
Original language | American English |
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Pages (from-to) | 2373-2388 |
Number of pages | 16 |
Journal | Journal of Physical Oceanography |
Volume | 46 |
Issue number | 8 |
DOIs | |
State | Published - 1 Aug 2016 |
Bibliographical note
Publisher Copyright:© 2016 American Meteorological Society.
NREL Publication Number
- NREL/JA-5000-67093
Keywords
- circulation/dynamics
- coastal flows
- estuaries
- geographic location/entity
- mixing
- shear structure/flows
- turbulence